1. Technical Field
The invention relates to the field of liquid crystal display technology, and more particularly to a method for repairing a hot pixel of a liquid crystal display panel and a liquid crystal display panel with a hot pixel being repaired.
2. Description of the Related Art
A liquid crystal display (LCD) is a flat, super thin display device, which consists of a number of colored or black-and-white pixels, being placed in front of a light or a reflecting plate. Due to advantages such as low power consumption, high definition, small dimension and lightweight, the liquid crystal display is prevalent and being the mainstream of display devices. Thin film transistor (TFT) liquid crystal displays are dominant in liquid crystal displays at present, a liquid crystal display panel is a main component of a liquid crystal display.
A liquid crystal display panel can consist of a thin film transistor array substrate, a colored filter substrate and a liquid crystal layer. Numerous pixel units are arranged on the thin film transistor array substrate in the form of an array, each pixel unit at least includes a thin film transistor and a pixel electrode assembled corresponding to the thin film transistor. The thin film transistor is connected to a scan line and a data line as a switch component that starts pixel units, voltage of data signals is loaded onto the corresponding pixel electrode by drive of scanning signals to realize the display of image information. Otherwise, part of the pixel electrode can cover the scan line or a common line of a substrate, lapping part is regarded as a memory capacitance Cst, utilizing for stabilizing voltage of data signals loaded on the pixel electrodes to ensure display quality of images.
A charge-share unit is employed into a pixel of a liquid crystal display panel in order to improve the display quality at wide angle, which means the colors at side view or front view are identical. FIG. 1 is a schematic structural view of an existing charge-share unit. As shown in FIG. 1, since charge-share technique is adopted, the pixel includes a main pixel unit, a sub pixel unit and a charge-share unit. The main pixel unit includes a main pixel electrode P1 and a first thin film transistor T1, the gate electrode of the first thin film transistor T1 is connected to a first scan line S1 electrically, the source electrode of the first thin film transistor T1 is connected to a data line D electrically, the drain electrode of the first thin film transistor T1 is connected to the main pixel electrode P1 electrically; the sub pixel unit includes a sub pixel electrode P2 and a second thin film transistor T2, the gate electrode of the second thin film transistor T2 is connected to the first scan line S1 electrically, the source electrode of the second thin film transistor T2 is connected to the data line D, the drain electrode of the second thin film transistor T2 is connected to the sub pixel electrode P2 by an antenna L, the antenna L passes across the main pixel electrode P1; the charge-share unit includes a third thin film transistor T3, the gate electrode of the third thin film transistor T3 is connected to a second scan line S2 electrically, the drain electrode of the third thin film transistor T3 is connected to the sub pixel electrode P2, a first charge capacitance Ccs1 is formed between the source electrode and the main pixel electrode P1, at the same time a second charge capacitance Ccs2 is formed between the source electrode and a corresponding common line COM. The equivalent circuit diagram of the charge-share unit is as shown in FIG. 2. Cgs1 is a parasitic capacitance of the main pixel unit, Cst1 is a memory capacitance of the main pixel unit, Clc1 is a liquid crystal capacitance of the main pixel unit; Cgs2 is a parasitic capacitance of the sub pixel unit, Cst2 is a memory capacitance of the sub pixel unit, Clc2 is a liquid crystal capacitance of the sub pixel unit.
Basic principle of charge-share technology is: firstly when the first scan line S1 sends scanning signals, the source electrodes and the drain electrode of the first thin film transistor T1 and the second thin film transistor T2 are connected, resulting in voltages of the main pixel electrode P1 and the second pixel electrode P2 attain the same potential influenced by data signals sending from the data line D; then when the second scan line S2 sends scanning signals, the drain electrodes and the source electrodes of the first thin film transistor T1 and the second thin film transistor T2 are cut off, at the same time the drain electrode and the source electrode of the third thin film transistor T3 are connected, resulting in charges on the sub pixel electrode P2 transfer to the common line COM by the second charge capacitance Ccs2, which can generate difference in voltage of the sub pixel electrode P2 and the main pixel electrode P1, and the liquid crystal of the sub pixel unit and liquid crystal of the main pixel unit deflect at different angles, which can achieve multi-domain display and offset color shift at wide angle.
The process of manufacturing a liquid crystal display panel includes manufacture and transportation, the entire process can produce plenty of particles, some of the particles will be swept by washers, and some of the particles will be left on the liquid crystal display panel (array side of CF side, an array substrate or a colored film substrate), the particles remaining on the liquid crystal display panel can cause hot pixels, hot (dead) lines, dotted hot pixels and dim hot (dead) lines when a liquid crystal display panel is lit, which are all not allowed to appear on a liquid crystal display panel. Therefore, the liquid crystal display panel will be repaired by a YAG laser, which can remove the particles, or hot pixels are adjusted to be dead pixels. To assure the quality of a liquid crystal display panel and sense of eyes, hot pixels are not permitted and the necessity of adjusting hot pixels into dead pixels is without doubt.
According to the charge-share unit shown in FIG. 1, when hot pixels appear in the sub pixel unit, the conventional method of adjusting hot pixels of the sub pixel unit to dead pixels is: referring to the schematic view of FIG. 3, first cutting the connection of the drain electrode of the second thin film transistor T2 and the antenna L, and cutting the connection line of drain electrode and the source electrode of the third thin film transistor T3 (marked by x in FIG. 3), then welding the sub pixel electrode P2 and the common line COM to be a short circuit (as L0 shown in FIG. 3), which can adjust a defective sub pixel unit to a dead pixel and enhance yield rate of liquid crystal display panels. In the method, potential of the antenna L in the sub pixel unit after repairing and that of the common line COM are equivalent, and the antenna L passes across the main pixel electrode P1, which can increase the memory capacitance Cst1 of the main pixel unit.
In a pixel unit, a feed through voltage ΔV can be generated after opening and shutting a thin film transistor constantly. To be more specific, according to the main pixel unit in the previous pixel, the feed through voltage
            Δ      ⁢                          ⁢      V        =                            (                      Vgh            -                          Vg              ⁢                                                          ⁢              1                                )                ⁢        Cgs        ⁢                                  ⁢        1                              Cgs          ⁢                                          ⁢          1                +                  Clc          ⁢                                          ⁢          1                +                  Cst          ⁢                                          ⁢          1                      ,where Vgh is a cut-in voltage of the first thin film transistor T1, Vg1 is a cut-off voltage of the first thin film transistor T1. FIG. 4 is an oscillogram of voltage signals received by a pixel unit, Vd in the figure is waveform of voltage driven by data signals, Vg is waveform of voltage driven by scanning signals, Vp is waveform of actual voltage signals received by the pixel electrode, Vcom is a common voltage signal. As shown in FIG. 4, as the existence of the feed through voltage ΔV, a voltage Vp of a fully charged pixel electrode is less than that of the driving voltage Vd in circumstances of no matter positive half period or negative half period of the data signals driving voltage Vd, and the different value is exact ΔV, and absolute values of different value of Vp and Vcom in the positive half period and that in the negative half period are the same. Therefore, to the main pixel unit, when the memory capacitance Cst1 increases, ΔV decreases according to the formula of ΔV above, when the common voltage Vcom maintains, the different value of Vp and Vcom increases (images are dim but frequency is high, dim light is hardly perceived) in the positive half period of data signal driving voltage Vd; the different value of Vp and Vcom decreases (images are bright) in the negative half period of data signal driving voltage Vd. The final appearance will be a subtle light spot. Therefore, after repairing the sub pixel unit, the influence on the memory capacitance Cst1 of the main pixel unit should be avoided.